Field of the Invention
The present invention relates to electromagnetic interference (EMI) filters in integrated circuit (IC) format incorporating electro-static discharge (ESD) protection components, and the manufacturing method
Description of the Prior Art
Electromagnetic interference (EMI) can affect electronic system performance, especially at electronic interfaces, e.g., Mobile Industry Processor Interface (MIPI), Universal Serial Bus (USB), High Definition Multimedia Interface (HDMI) and Mobile High-Definition Link (MHL), etc., which feature very high data transmission rates and very broad frequency bandwidth. Low-pass filters (LPF) can be used to block EMI interferers (or, noises) transmitting in both directions at the interfaces of electronic products. Critical specifications (i.e., specs) for EMI filters include low pass-band insertion loss (IL), high cut-off frequency (fC), wide pass-band spectrum and high rejection-band attenuation. Low pass-band IL ensures minimum signal loss within the application frequency band. The cut-off frequency is defined by the frequency corresponding to the −3 dB insertion loss point of the useful signals. Pass-band allows the useful signals pass through and determines how many harmonics of the useful signal can be kept.
A wide pass-band allows high data-rate and ensures high level of signal integrity. Rejection-band generally covers the 800 MHz to 6 GHz frequency spectrum, corresponding to the carrier band frequencies of typical radio-frequency (RF) applications. −30 dB attenuation in the rejection-band is usually required to reduce the noise level by a factor of 1000 in power scale, meaning a high signal-to-noise ratio (SNR) of electronic systems.
In electronic products, noises can be generated within the systems or injected into the systems externally through various data interfaces (USB, HDMI. DVI, MIPI, etc.), which affects the useful signals and results in performance degradation of high-speed electronics. To alleviate the ever-increasing noise interfering problem within high-speed electronics, differential signal processing techniques are used in modern electronic systems, for example, low voltage differential signaling (LVDS), where the large common-mode noises can be removed while processing the small useful differential signals.
Common-mode filter (CMF) technique can be used to remove common-mode noises, while allowing the useful differential signals passing through with minimum loss. This is particularly critical to contemporary high-frequency and high-speed electronics, such as, high-definition displays, smart-phones, high-resolution cameras, and communication links with beyond giga bits per second (Gbps) data rates, etc. Existing CMF filter components, often called common-mode choke coils, include wire-wound type formed by winding copper wire around a ferrite core and laminate-type created by forming alternatively insulating layers and metal thin-film coil conductors on magnetic substrate through thin-film processing techniques. These common-mode choke coils are essentially discrete CMF components fabricated using various discrete component processing techniques, which translates into relatively large and thick footprint, hence making them not suitable for advanced electronic apparatus, such as smart-phones, which require very thin and small CMF components with very high performance.
In principle, a CMF device is a passive transformer, as shown in FIG. 1, with two coils, a primary coil and a secondary coil, formed close to each other so that the magnetic flux can be coupled into the two coils as much as possible. The critical performance specs for CMF are apparently high common-mode rejection and low differential-mode loss. To this end, a magnetic core, or, preferably a closed-loop magnetic circuit path, is used to direct the magnetic flux in order to suppress any magnetic loss. Hence, close and efficient magnetic coupling is required for high-performance CMF components, which can be easily implemented in fabricating discrete common-mode choke coils as mentioned above.
On the other hand, low insertion loss of common-mode choke coils require very low series resistance of the metal coils, which may be readily achieved in fabricating wire-wound and laminate CMF components by using thick metal layers. For these reasons, ferrite and ceramics based discrete CMFs have been widely used so far. However, these discrete type common-mode choke coils suffer from relatively low common-mode noise attenuation across the 700˜2500 MHz spectrum, typically used for mobile devices today. In addition, today's mobile electronics feature extremely high system integration, which requires integration of CMF filter with ESD protection structure that cannot be realized using the abovementioned discrete type common-mode choke coils.
On account of above, it shall be obvious that there is indeed an urgent need for a common-mode EMI filter in IC format with integrated ESD protection being proposed nowadays.